First, is that the delivered pressure, or do you have a PRV already and no expansion tank. That is a very high pressure for the utility to be delivering to you. What is your pressure immediately after you run some water?
If the utility is delivering 140 psi water then they have a problem. Either that or you live in the low area of a very hilly city.
If the pressure is down after you run the water, and then comes back up in 5 minutes or so, you probably have a bad PRV. If it comes up only after you have used hot water and it takes 30 minutes or more, then you probably need an expansion tank, or your expansion tank has failed or is full of water because it has no air.
Several people have said they have a problem with pressure loss with some PRVs. You want to make sure that what you get is big enough. Are you planning to get the same model that has been giving you good service until now?
To change the PRV you will need to get the water supply shut off. If the PRV is after a valve that you can shutoff, then it should be easy enough. Try to find one that has the same end fittings.
If it is not after your shutoff valve, then you will need to get the utility to shut it off.